Americans seeking to visit Cuba must navigate a complicated maze of travel, commerce and financial restrictions unveiled Wednesday by the Trump administration, part of a new policy to further isolate the island's communist government.

Now off-limits to United States citizens are dozens of Cuban hotels, shops, tour companies and other businesses included on a lengthy American blacklist of entities that have links to Cuba's military, intelligence or security services.

And most Americans will once again be required to travel as part of heavily regulated, organised tour groups run by US companies, rather than voyaging to Cuba on their own.

The stricter rules mark a return to the tougher US stance towards Cuba that existed before former President Barack Obama and Cuban President Ra?l Castro restored diplomatic relations in 2015. They come as Donald Trump tries to show he's taking action to prevent US dollars from helping prop up the Cuban government.

"These measures confirm there is a serious reversal in bilateral relations which has occurred as a result of the decisions taken by the government of President Donald Trump," said Josefina Vidal, the top Cuban diplomat for North America.

Still, the policy is only a partial rollback of Obama's changes. Cruise ship visits and direct commercial flights between the countries will still be permitted. Embassies in Washington and Havana stay open.

The rules are designed to steer US economic activity away from Cuba's military, intelligence and security services, which dominate much of the economy through state-controlled corporations.

The goal is to encourage financial support for Cuba's growing private sector, said senior Trump administration officials, who briefed reporters on a conference call, on condition they not be quoted by name.

To that end, the US Treasury Department said it is expanding and simplifying a licence that allows some US exports to Cuba despite the embargo. They include tools and equipment to build or renovate privately owned buildings.

"We have strengthened our Cuba policies to channel economic activity away from the Cuban military and to encourage the government to move towards greater political and economic freedom for the Cuban people," Treasury Secretary Steven Mnuchin said.

The administration took several months to finalise the details of the new rules, which will take effect Thursday.

The new policy, first announced in June, maintains several categories of travel to Cuba that are permitted despite the embargo, which carries on decades after the Cold War's end. Americans can still travel on educational and "people to people" trips, as well as visits designed to support the Cuban people by patronising privately owned small businesses that have popped up across the island in recent years.

But those travelling to support Cuba's people must have a day-long schedule of activities designed to expose them to Cubans and steer dollars towards citizens, such as renting rooms in private homes. Those on organised, 'people to people' or educational visits must be accompanied by a representative of the US-based group organising the trip.

Vidal, the Cuban diplomat who was the public face of Cuba's opening with the United States during the Obama administration, said the policy would harm Cuba's economy, American citizens and US businesses.

The rules were also quickly denounced by travel groups and proponents of closer US ties to the island.

"Cuba is still open for business," said Charel van Dam of the Cuba Travel Network. "It is still possible for people to travel, but I think these announcements will serve mainly as something to scare off people who want to visit."

Senator Patrick Leahy, D-Vermont, a vocal advocate of improved US-Cuban relations, noted the announcement came as Trump was in China pushing more US business engagement with another communist-run country. "The hypocrisy of the White House ideologues is glaring," Leahy said.

It's unclear how aggressively the US will police the new rules. Officials said they would use information obtained from several US agencies to catch violators, who could be subject to penalties and criminal prosecution.

The blacklist bars business with the large military-run corporations that dominate the Cuban economy. These include GAESA and CIMEX, holding companies that control most retail business on the island; Gaviota, the largest tourism company; and Habaguanex, which runs Old Havana.

It also targets a new cargo port and special trade zone outside the city of Mariel that has been the focus of Cuba's efforts to draw foreign investment in manufacturing and distribution.

Blacklisted hotels include the Manzana Kempinski, which opened with great fanfare this year as Cuba's first to meet the international five-star standard.

The overall impact on American business with Cuba will likely be limited. Trade is sparse. Many American travellers already stay at hotels not on the no-go list, and the company that imports most American food products to Cuba is similarly unaffected.

Bringing home limited quantities of rum and Cuban cigars is still allowed, officials said.